Submitted to: Journal of Dairy Science
Publication Type: Abstract only
Publication Acceptance Date: 2/28/2005
Publication Date: 7/24/2005
Citation: Norman, H.D., Hutchison, J.L., Kuhn, M.T., Wright, J.R., Hare, E. 2005. Selection intensity for yield traits, somatic cell score, and days open when culling dairy cows [abstract]. Journal of Dairy Science. 88(Suppl. 1):140. Interpretive Summary:
Technical Abstract: Traits emphasized when culling cows from the herd should be similar to those considered when selecting bulls for matings. Emphasis given by dairy producers to different yield and fitness traits when culling cows was documented, and trends since 1980 were determined. Least-square estimates for survivor groups provided first-parity differences for milk, fat, and protein yields; somatic cell score (SCS); and days open (DO) between cows that calved for additional lactations and those that were culled. Trait differences also were expressed on a standardized basis by dividing the least-square estimate by the phenotypic standard deviation for the trait. Cows with 2, 3, or >=4 parities had an advantage of 900 to 1100 kg of first-parity milk over those culled before second parity; only a small advantage was found for cows with >=3 parities compared with those with 2. Superiority of cows kept in recent years to culled cows has declined considerably, not only for milk yield but for fat and protein yields, SCS, and DO. On a standardized basis, the most intense selection from 1980 to 1995 was for protein and milk yields (0.80 to 0.90); selection intensity was lower for fat yield (0.54 to 0.75), SCS (0.29 to 0.53), and DO (0.29 to 0.45). Cows that survived >=2 parities had lower first-parity SCS than those with only 1 parity. Likewise, those with >=3 parities had lower first-parity SCS than those with only 2 parities, and those with >=4 had lower SCS than those with only 3. Cows with only 2 parities had the highest mean DO during first parity followed by those with only 3, those with >=4, and those with only 1; those with only 1 parity had 20 to 27 fewer DO than those with >=2 parities. Knowledge of which traits dairy producers emphasize in culling cows can assist artificial-insemination organizations in determining which traits should be emphasized when choosing young bulls and graduating progeny-test bulls.